Most cathodoluminescent displays are produced by a number of different methods that deposit a granular phosphor onto a conductive glass substrate. These known methods of phosphor deposition incorporate a patterning process to provide multicolors, such as red, green and blue phosphor dot clusters or stripe clusters, which create a spectrum by color addition. However, there are a number of disadvantages inherent in screens produced by these known methods.
One disadvantage is that the light generated in each grain comes out in all directions. This has a number of undesirable consequences. For example, because not all the light comes out to the viewer, there is a significantly lower usable light efficiency. In addition, the light which scatters into neighboring grains results in decreased spatial resolution of the screen. Finally, the light that scatters into neighboring grains can excite these neighboring grains and cause them to radiate different, unwanted colors or at least unwanted radiation so that spatial and chromatic resolution is decreased.
With the prior art displays, it will also be appreciated that the electron beam can scatter into neighboring grains which results in a number of deleterious consequences. For example, such scatter can excite neighboring grains so that spatial resolution is decreased or different colors are introduced. In addition, electrons deposited from the electron beam on to the phosphor screen can significantly charge up the non-conducting phosphor. One consequence of this charging up is that the incident electron beam is deflected to neighboring grains instead of hitting its intended target grain, thereby decreasing spatial resolution. Another consequence of charge up is that the impinging electron energy distribution is significantly spoiled, thereby decreasing light output and light output uniformity. Additionally, if the phosphors are allowed to charge up too much, the charged phosphor screen can catastrophically break down (voltage breakdown). This breakdown problem results in flickering, non-uniform brightness and blooming resulting from both the dispersion in the impinging electron energy and the redirection of the electron trajectory. Finally, the charge-up of the phosphor, which creates charge-induced defects, can change the cathodoluminescent properties and lower the useful lifetime of the phosphor.
A further disadvantage of the existing process of phosphor deposition is the fact that the phosphor discharge path is long. This means that a relatively high energy electron beam is required. Also, the boundary between different colors is very hard to control.
It will be appreciated from the foregoing that the production of a cathodoluminescent display screen by the existing process of phosphor deposition onto a glass substrate is limited in terms of the clarity of the image produced.
In U.S. Pat. No. 4,857,799 (Spindt, et al), the use of field emission cathodes for providing an electron stream to a flat screen cathodoluminescent display coated with luminescent phosphor is disclosed. The cathodes are incorporated into a display backing structure.
In U.S. Pat. No. 4,277,114 (De Jule), the use of a cathodoluminescent display panel which incorporates a gas discharge device is disclosed. The gas is under pressure and the use of phosphor disposed on the transparent walls of the cavity surrounding a positive column is disclosed. The disclosed device uses plasma to generate an electron stream.
In U.S. Pat. No. 4,103,204 (Credelle), the use of a group of channels for directing an electron path is disclosed. A gun structure selectively injects electrons into the channels and slalom focusing is used to guide the electrons down the path to the display device. The use of a channeling technique is provided to improve picture quality.
In U.S. Pat. No. 3,992,644 (Chodil, et al) a cathodoluminescent device is disclosed which displays colors. The disclosed device uses a hollow cylindrical cathode shell and an anode that is flush with the shell.
Field emitter arrays which are designed for row-column addressability of general interest are disclosed in the following U.S. Pat. Nos.: 4,578,614 (Gray, et al), 4,307,507 (Gray, et al) and 4,513,308 (Greene, et al).